Electronic fuel injection systems are well known in the art. Generally, the electronic control is utilized to determined the appropriate amount of fuel which is injected, as well as the appropriate timing of the injection for most effective combustion of the injected quantity. An electronic control module receives information from various sensors which indicate the engine operating conditions, for example, the operator's request (throttle position), the vehicle speed, intake manifold pressure, etc., and the amount of fuel is determined based upon the received information. The appropriate injection timing is also determined by the control module based upon various operating conditions including (in addition to those mentioned above) the fuel quantity (fueling) to be injected. The fueling and timing are updated periodically to correct or adjust the timing as the operating conditions change. Typically, the electronic control unit also includes maximum limits for timing and fueling to ensure that the maximum rated loads of various engine components are not exceeded.
It is constantly a goal to provide an improved control system for engine fueling (i.e., fuel quantity) and timing to make most efficient use of the fuel injected, thereby improving the fuel economy. In addition, it is extremely important to control fueling and timing to minimize exhaust pollutants and meet increasingly stringent emissions standards. Proper fueling and timing is also necessary to prevent engine overloads thereby avoiding repairs and improving the durability of the engine.
U.S. Pat. No. 4,379,332 to Busser et al. discloses an electronic fuel injection system in which a plurality of sensors provide operating information to an electronic control unit, which then computes the fueling and timing operation of the fuel injectors. In determining the fuel quantity parameter, the lesser of a full load fuel quantity and a percent load fuel quantity is selected, with the percent load fuel quantity determined by the sum of a proportional component and an integral component. The proportional component is calculated as a function of the actual engine speed and a commanded engine speed, and the integral component is related to a cumulative speed error, with the speed error defined as the difference between the commanded speed and actual speed signals. The timing is obtained by summing first and second quantities, one of which is a function of the actual engine speed and the calculated fuel quantity, and the other is a function of air temperature. The above proportional components, full load quantity, and first and second timing quantities utilize two or three dimensional surfaces (graphs or maps) which are interpolated for various inputs of the electronic control unit. Thus, Busser et al. perform a series of computations and combine calculated and mapped values to arrive at final calculated fuel injection quantity and timing values.
Often, it is difficult, if not impossible, to utilize complex computations to achieve the most desirable fueling and timing for a wide range of operating conditions, particularly where emissions standards, fuel economy and engine durability are important concerns The primary difficulty in utilizing formulae for calculating fueling and timing resides in deriving a mathematical relation which accurately models actual engine operation, and which can accommodate or evaluate trade offs associated with economy, performance, emissions and durability requirements. The use of three dimensional graphs, maps or look-up charts can be particularly useful where it is desired to select fueling and timing values which are empirically known to be particularly suitable for various sets of operating conditions. Utilizing maps or tables, the engine fueling and timing can be selected based upon known values which more optimally achieve certain characteristics, e.g. performance, while operating within other restraining characteristics, e.g. emissions or economy. However, even utilizing maps or tables, it is extremely difficult to include all possible sets of operating conditions or to consider all factors relevant to controlling fuel injection.
U.S. Pat. No. 4,368,705 to Stevenson et al. discloses an engine control system in which a series of maps are utilized to control the timing, with the map selection based on the mode of operation of the engine. A timing map selector is provided which receives signals from various engine sensors and in response, selects a particular map for control of the timing. The timing is then determined for the corresponding operating conditions within the selected mapped timing relation. Thus, a wider range of conditions or situations can be considered since separate maps are provided for different operating modes.
In Stevenson et al., basically four operating maps are provided. One map is utilized for initial engine operation to accommodate for operation of a cold engine. A transient map is selected where the operator has made a substantial change in the throttle position indicating the operator desires significant acceleration or deceleration. In addition, urban and highway maps are also provided.
However, the control system required for selecting a particular map can be extremely complicated and it is possible that certain conditions or driving habits could cause an erroneous map selection. For example, in Stevenson et al. an urban condition detector generates a signal upon concurrence of a throttle position change signal and an engine speed change signal, and the signals from the urban condition detector are then counted. If the count exceeds a predetermined number during a preset time period, an urban driving map is selected. A highway map is selected where the count is below the predetermined number. A nervous or fidgety driver may often change speeds and throttle positions even during highway driving, yet due to the urban detector, an urban driving map may be selected.
Another difficulty with the Stevenson et al. arrangement is that a slight change in operating conditions may change the selected map which may cause a more dramatic change in the performance or response of the engine than the change in conditions would warrant. For example, where the count (by the urban detector) of concurrent speed change and throttle position change shifts from just below the predetermined number to just above the predetermined number, a significant change in the performance or response of the engine could result (as the selected map changes) from only a small change in engine operating conditions or commands by the driver.
Whether a single map or a plurality of maps is utilized, each map must accommodate a range of conditions. For example in Stevenson et al., the highway/urban maps must accommodate speed change conditions for the ranges on either side of the predetermined count number, and the maps must therefore be somewhat conservative in approaching performance limits to accommodate constraints with regard to durability, economy or emissions. Thus, while the use of several maps is advantageous in that additional factors may be accounted for in selecting a map which is more desirable for a determined mode of operation, each map must nevertheless accommodate a range of conditions within a particular mode. Furthermore, a small change in the operating conditions may result in a determination that the operational mode has changed resulting in a magnitude of response which is larger than the actual change of operation.
As an illustration of the difficulty in accommodating numerous different conditions and in selecting a correct map, in determining whether the transient map is to be utilized, the selector in Stevenson et al. simply determines whether a dramatic change has been requested, not the magnitude of the change or its relation to previous engine operation (i.e., how the present operating conditions compare to operating conditions over a recent period of time). Thus, as long as the change is above a certain predetermined value, such that it is "dramatic," the response in selecting the transient mapped values is the same regardless of how "dramatic" or extreme the change is. Where the change is only slightly below the predetermined value, the condition is treated as non-transient, even though it may be very similar to conditions where the change is just above the predetermined "dramatic" value which is handled by the transient map.
Further, in Stevenson et al., the transient map is selected only for a large or substantial change in throttle position, and the urban map is selected only where speed and throttle position change concurrently in sufficient frequency. The steady highway map is selected where throttle position change is not substantial, and where throttle changes are not accompanied by speed changes of sufficient frequency. However, such a categorization by the map selector may result in selection of an urban condition map where the operator has changed the throttle position to accommodate for upgrades and downgrades if it is accompanied by a concurrent speed change, even though such a condition might more appropriately be treated as transient or highway. In addition, a somewhat transient condition may exist even when the throttle position is constant, for example where the speed changes significantly as a result of upgrades and downgrades, however the transient map would not be selected, since in Stevenson et al. only a substantial change in throttle position is utilized as a basis for selecting the transient map.
As demonstrated above, complicated systems have been developed for controlling fuel injection to accommodate a variety of operating conditions. However, it continues to be a goal to develop improved systems for controlling fuel injection which can react to a wide range of operating conditions, such that most effective use can be made of the fuel while providing more optimal operation considering durability, performance, emissions and economy requirements.